An innovative automotive electronic circuit protection design

    Automotive electronics is a hot development area at present. The booming development of China's automobile market has brought new opportunities to the local automotive electronics industry. More and more companies have increased their investment in automotive electronic products. A large number of local design and manufacturing companies for automotive electronic products, including ECU, ABS, DVD, GPS, HVAC, CANBUS, etc., have sprung up like mushrooms after rain, which has also opened up a new world for electronic component manufacturers engaged in circuit protection design.

　　Safety and reliability are of utmost importance

　　A fuse is a passive device, similar to a switch. When a product fails or an accident occurs, the fuse needs to be able to safely disconnect the power supply without generating smoke or flames, and without endangering the life of the operator. Therefore, no matter what electronic product, it is usually equipped with a fuse without exception, which is also the guarantee of the safety of electronic products.

　　For fuses, the most important reference indicators are safety and reliability, that is, they must not be disconnected during normal operation, and must be disconnected immediately when a fault occurs in the subsequent stage. Fuses have only two working states: on or off. To ensure the safety and reliability of the entire system, the fuse itself must first meet these two points. Good fuse design and application are essential and a delicate science.

　　When selecting a fuse, circuit designers should consider two aspects: static and dynamic. Static refers to voltage, current, ambient temperature, size, failure current, etc.; dynamic refers to fusing time, melting heat value, etc., which are the key points in the selection and design of fuse products. Secondly, after theoretical calculation of the fuse, it is necessary to combine it with on-site testing and verification, and finally reach an ideal design plan with the help of reliability analysis.

　　Innovative automotive circuit protection design

　　Circuit protection is everywhere in cars, especially now that car bodies are using more and more intelligent electronic devices, turning the previous pure car machinery into a "running robot" with a soul. For electronic products, safety is the top priority, so fuses in car circuits have become integrated and miniaturized.

　　In the development of automotive electronics, almost every electrical device needs a fuse, usually called cable protection. The main function of the fuse is to limit the increase of current. When an accident occurs (such as a power short circuit caused by a car accident), the large current generated at this time requires the fuse to immediately cut off the main power supply to avoid further danger. The protection structure of traditional automotive cable fuses is multi-pole and layered, but when the lowest level of electronic equipment fails, only the fuse of the unit with the fault is broken, and it will not affect the circuit of the upper level. However, in the process of car modification, for example, when a high-power audio is added to the outside, its power comes from the body battery. If the fuse is used improperly and is not disconnected when it needs to be disconnected, these minor faults will affect the reliability of the entire vehicle system and cause the fuse to malfunction. Therefore, good fuse design and selection are particularly important.

　　Littelfuse's latest circuit protection products are designed for automotive controller area network (CAN) applications.

    To this end, the novel integrated fuse (Masterfuse) has been incorporated into the design of automotive electronics, which integrates the overcurrent protection of the entire body to achieve a higher level of protection. The integrated fuse product is a configurable fuse solution with a variety of different fuse types (i.e. MEGA and MIDI) and ratings in a compact package. This packaged fuse allows users to replace multiple discrete fuses in the distribution box with one component, thereby eliminating the bolts, busbars and connecting wires currently required. By reducing the number of required joints, the entire system increases reliability while reducing costs. Each integrated fuse can be customized according to the user's application to obtain the most optimized circuit protection package product.

　　Integrated fuse

　　On the other hand, there is another type of synchronous overvoltage protection device TVS that is also worthy of attention. Because in automotive electronics, all electronic devices are facing the threat of static electricity (ESD) and load mutation (LOADDUMP), these overvoltage problems will cause permanent damage to the chip circuit, so overvoltage protection is essential. At the same time, meeting these requirements is also part of the ISO7637 standard. In this regard, Littelfuse automotive-grade TVS tubes meet the above requirements to ensure the safety and reliability of automotive electronic equipment. In fact, the application of TVS is already relatively common, and long life and high reliability operation are the performance that automotive-grade TVS must have, such as passing AEC-Q101 certification to meet the requirements of vehicle operation.

　　Taking the automotive electronic ESD protection solution as an example, due to the extensive application of buttons and USB interfaces, the test specifications are constantly upgraded. The electrical protection requirements of the ISO10605 standard have even reached 25KV. Without a reliable circuit protection device, this requirement cannot be met. Littelfuse's semiconductor protection array can meet the ESD test requirements of the entire circuit. For example, SP1003 can reach the test index of 30KV, and each circuit is connected in parallel with one of the protection devices to protect automotive electronics. In addition, in terms of data line protection, the widespread use of CAN bus in automobiles connects all electronic components together for data exchange. For the protection of CAN chips, Littelfuse's dedicated protection devices provide an ideal form of protection, which can not only meet ESD protection, but also meet some surge protection requirements. For example, the typical application circuit of the SM24CANA series provides dual protection of common mode and differential mode.